The present invention relates to a method for the preparation of a catalyst or catalyst precursor, the catalyst or catalyst precursor obtainable by the method, and to the use of such catalyst in a process for producing normally gaseous, normally liquid and optionally solid hydrocarbons from synthesis gas generally provided from a hydrocarbonaceous feed, for example a Fischer-Tropsch process.
Many documents are known describing processes for the catalytic conversion of (gaseous) hydrocarbonaceous feedstocks, especially methane, natural gas and/or associated gas, into liquid products, especially methanol and liquid hydrocarbons, particularly paraffinic hydrocarbons. In this respect often reference is made to remote locations and/or off-shore locations, where direct use of the gas, e.g. through a pipeline or in the form of liquefied natural gas, is not always practical. This holds even more in the case of relatively small gas production rates and/or fields. Reinjection of gas will add to the costs of oil production, and may, in the case of associated gas, result in undesired effects on the crude oil production. Burning of associated gas has become an undesired option in view of depletion of hydrocarbon sources and air pollution.
The Fischer-Tropsch process can be used as part of the conversion of hydrocarbonaceous feed stocks into liquid and/or solid hydrocarbons. Generally the feed stock (e.g. natural gas, associates gas and/or coal-bed methane, coal) is converted in a first step into a mixture of hydrogen and carbon monoxide (this mixture is often referred to as synthesis gas or syngas). The synthesis gas is then fed into a reactor where it is converted in one or more steps over a suitable catalyst at elevated temperature and pressure into compounds ranging from methane to high molecular weight modules comprising up to 200 carbon atoms, or, under particular circumstances, even more, (and water).
Catalysts used in the Fischer-Tropsch synthesis often comprise a carrier based support material and one or more metals from Group VIII of the Periodic Table, especially from the cobalt or iron groups, optionally in combination with one or more metal oxides and/or metals as promoters selected from zirconium, titanium, chromium, vanadium and manganese, especially manganese. Such catalysts are known in the art and have been described for example, in the specifications of WO 9700231A and U.S. Pat. No. 4,595,703.
Catalysts can be prepared by obtaining a metal hydroxide, carefully oxidising it to the metal oxide and then placing it in the appropriate reactor where it is reduced to the metal in situ.
One catalyst for Fischer-Tropsch reactions is cobalt in titania. In one way to prepare the catalyst, cobalt hydroxide (Co(OH)2) can be used as a starting material. This material is dried, calcined and then decomposed to form cobalt oxide (CoO). It is then impregnated onto a support, for example titania. The cobalt is further oxidized (CO3O4) and then placed in a Fischer-Tropsch reactor. In the reactor the cobalt oxide is reduced to cobalt.
Hitherto, there has been no consideration of control over the combination of the catalyst metal such as cobalt, and a promoter(s). Thus, the present combinations made have a relatively wide variation of concentrations of the constituents in each unit or crystal of catalyst formed. Such varied material therefore requires a wide variation in the conditions, especially temperature, for reduction of the (precursor) catalyst material to provide the elemental cobalt on the support carrier. But, a wide variation in reduction conditions also leads to some catalyst forming other (unwanted) species, e.g. cobalt titanate, which cannot catalyze and is therefore unproductive. To avoid such unwanted species, it has been preferable to minimize the variation in reduction conditions, even though at least some of the catalyst or catalyst precursor will not become activated. The loss of potential activity is currently accepted as necessary wastage in the art.
However, control of the co-formation of the, for example, cobalt and a promoter(s) would enable a more controlled reduction activation process. This would lead to a decrease in the wastage of cobalt that is not suitably transformed into elemental cobalt. That is, an increase in the amount of catalyst material that is properly formed and activated, hence an increase in the efficiency of the catalyst material per volume of support carrier, and hence, in many ways, an increase in the efficiency and production of the overall process and reactor.